The major results of this study of thinhorn sheep evolution and behaviour have come from investigations of (i) the impact of glaciation on evolutionary history, (ii) the potential for MC1R to determine coat colour darkness, (iii) the role of colour as an indicator of quality, (iv) the relationship between horn growth rate and longevity and (v) behavioural reactions of sheep to human disturbance. I have found that hybridisation is a more important factor in mountain sheep evolutionary processes than previously thought. Contact between bighorn (O. canadensis) and thinhorn sheep (O. dalli) occurred prior to the last ice age which appears to have resulted in a zone of unique phenotypic colour variation. I attempted to determine whether colour variation is determined by the melanocortin 1 receptor (MC1R) gene. However, there was no evidence to suggest a relationship between individual darkness and mutations in MC1R. Behavioural evidence from sheep in central Yukon demonstrated that facial darkness is a good indicator of individual quality in rams, although I did not verify its use as a signal. Horn growth rate was negatively correlated with longevity indicating that a trade-off exists between these two traits that affect individual mating success. Finally, human generated disturbance resulted in differing reactions in thinhorn sheep genders and age classes.